Cell Wall Hydrolases

Many bacterial species possess more than one enzyme that hydrolyzes the same bond, a fact that complicates the determination of their biological role(s). This redundancy also contributes to the common thought of assigning a basic role to lytic enzymes in the biology of bacteria. The activity of some pneumococcal murein hydrolases (MHs) appears to be constrained by the membrane lipoteichoic acid (LTA) at the posttranslational level. Cell wall hydrolases (CWHs) of Streptococcus pneumoniae show both substrate and bond specificities. The lytA gene encodes the major S. pneumoniae autolysin (amidase) and represents the first example of a bacterial autolytic gene that was cloned and expressed. LytB is most probably a glucosaminidase capable of degrading Ch-containing cell walls. All the pneumococcal CWHs described have been shown to possess an absolute requirement for the presence of Ch for activity. The cloning of lytA has facilitated the isolation of the genes encoding the cell wall lytic enzymes from pneumococcal bacteriophages based on sequence homologies. This global analysis led the authors to propose that pneumococcal cell wall lytic enzymes could be the result of the fusion of two independent functional domains. The construction of active chimeric proteins between lysins of phage and bacteria led to new enzymes exhibiting novel properties that were, as expected, a combination of those showed by the parental enzymes.